In the past one or two decades, mobile communications terminals (e.g. mobile phones, user equipments, mobile stations, personal digital assistants, pocket computers and the like) used for exploiting the communications capabilities offered by mobile communications networks have experienced great improvements in performance.
An aspect that, in particular, has been improved concerns the operating autonomy of the mobile communications terminal.
Mobile communications terminals are in fact powered by batteries: the improvements in battery technology, in conjunction with the reduction of power consumption by the electronic circuitry of the mobile communications terminals, have significantly extended their operating range.
Nonetheless, the time operability of mobile communications terminals is still relatively limited, and this continue to represent a problem to be faced.
Typically, the responsibility of checking the battery charge level, and, depending on it, taking a proper conduct so to avoid ending with an unusable mobile terminal due to full battery discharge, is totally up to the user.
Completely relying on the fact that the user pay the due attention to this aspect is not particularly effective, nor particularly safe. In fact, nothing ensures that the user realizes in due time the low level of the battery charge and, in view of, e.g., his/her needs in the immediate future, adopt the correct conduct, by for example recharging the battery, or limiting the mobile communications terminal usage.
Additionally, it may happen that when the user realizes of the low battery charge condition, the battery level is already so low that the charge left is at best sufficient for placing/sending only one single voice call/message; this is in particular true when the battery has already been submitted to several charge/discharge cycles, considering that batteries degrade with time, so that an old battery may exhibit a faster charge fall than a new one.
In U.S. Pat. No. 6,236,326 a wireless telephone is described that when the battery nears depletion, and if a telephone call is not in progress, contacts the wireless telephone network and enables a call forwarding to a different number; if instead a telephone call is in progress, the wireless telephone plays an audible message to the party with whom the wireless subscriber is speaking, thereby informing the party that the wireless connection will soon be lost.
U.S. Pat. No. 6,704,583 describes a mobile telephone including a memory storing telephone numbers, and a controller detecting a telephone number of an incoming call, comparing the detected telephone number to the numbers stored in the memory, and determining whether the incoming call is to be received, even when a voltage supplied by the voltage source is equal to or lower than a predetermined threshold.
Solutions in which a mobile communications terminal provides to the mobile communications network indications about the battery charge have been proposed in the art.
For example, in WO 98/26622 the problems of call drops is faced. A mobile communications apparatus monitors the power level of its internal battery power supply, and the measured power levels are reported to and stored by the base station or switching node of a serving network. If an ongoing call should then be dropped, the stored power levels reported by the mobile communications apparatus engaged in the dropped call are retrieved and processed to determine whether the battery failure is a likely cause of the call drop: in the affirmative case, an appropriate cause notation is made in association with a recording of the instance of the call drop.
U.S. Pat. No. 6,408,172 is concerned about emergency calls placed within a cellular network. A battery status indicator associated with a calling mobile station during an emergency call is transmitted to the emergency center; the emergency center can provide special handling for such calls, such as displaying the low battery indicator to the emergency operator; in addition, the cellular network serving the mobile station can handover the call to a cell with lower power demands in order to prolong the battery life of the mobile station.
WO 98/10610 proposes a method for systematically scaling back the operations of a mobile station as its battery is continuously discharged by usage. Different mobile station operations are progressively disabled as the capacity of the battery falls below certain predetermined threshold levels: below the highest threshold level the mobile station sends a registration cancellation message to the serving system so as to prevent the receipt of any page message, then disables the transmit operation and enables only the receive operation. Below the lowest threshold level the mobile station does not completely shut off all operations, but instead allows the continuation of a minimum subset of operations, including the charging operation.
In EP 915 632 a base station of a wireless communications system receives battery power level information and other setup information from mobile stations operating within the service area of the base station during call setup procedures. Based on the battery power level information and other setup information, the base station assigns frequency channels to the mobile stations so that those mobile stations having battery power levels below a threshold value are assigned frequency channels that have lower interference levels than frequency channels assigned to other mobile stations. The frequency channel assignments are transmitted to the mobile stations.
In U.S. Pat. No. 6,072,784, scheduling priorities in a CDMA (Code Division Multiple Access) wireless communications system are adapted to conserve battery power in mobile terminals operating within the system. The transmit power of all mobile stations is controlled by the base station (which receives the battery power level information during call setup procedures) to optimally conserve the battery power of a particular mobile station reporting a low battery condition. The base station adapts scheduling priorities for the mobile terminals to expedite wireless transmission from those mobile terminals reporting low battery power levels.